Process for the production of composite ingots of magnesium containing prealloys

ABSTRACT

Compact, magnesium containing prealloy ingots are produced by casting a molten magnesium containing prealloy around prefabricated solid pieces of a prealloy having the same or similar composition as that of the molten prealloy. The resulting compact prealloy ingots are used in the production of cast iron with spheroidal graphite.

United States Patent llelner Trager Neu Isenburg;

Inventors Albert Kaune, Frankfurt; Horst Muhlberger, Frankfurt; Karl Josei Reifierscheid, Petterweil; Ludwig Grimm, Hart (All); GerhardWagner, Unterneukirchen-I-lart; Heinrich I-Iaslinger, Garching (Alz),all of, Germany 672,163 Oct. 2, 1967 Sept. 14, 1971 Appl. No. FiledPatented Assignees Metallgesellschalt Aktlengesellschalt Frankfurt/Main,Germany; Suddeutsche Kalkstick-stoplwerke A.G.

Trostbert, Germany Priority Germany M 71156 and M 75554 PROCESS FOR THEPRODUCTION OF Oct. 4, 1966, Sept. 15, 1967 COMPOSITE INGOTS OF MAGNESIUMCONTAINING PREALLOYS 8 Claims, 1 Drawing Fig.

u.s. c1

Primary Examiner-R. Spencer Annear Attorney-Stephens, I-Iuettig andO'Connell ABSTRACT: Compact, magnesium containing prealloy ingots areproduced by casting a molten magnesium containing prealloy aroundprefabricated solid pieces of a prealloy having the same or similarcomposition as that of the molten prealloy. The resulting compactprealloy ingots are used in the production of cast iron with spheroidalgraphite.

PROCESS FOR THE PRODUCTION OF COMPOSITE INGOTS OF MAGNESIUM CONTAININGPREALLOYS BACKGROUND OF THE INVENTION Magnesium containing prealloys areused in the preparation of cast iron with spheroidal graphite for thedeoxidation or desulfurization of cast iron in which the graphite whichseparates out upon the cooling of the molten iron is in spheroidal form.(See US. Pat. Nos. 3,328,164; 3,306,707; 3,030,205; 2,762,705 andco-owned and now abandoned US. Pat. application Ser. No. 653,661, filedJuly 17, 1967, in the names of Horst Muhlberger and Herbert Knahl.)

It is known to use the magnesium containing prealloys in socalledimmersing bell jars or plunging cups and to treat cast iron meltstherewith in dipping or immersing processes for the purpose of producingcast iron with spheroidal graphite (see US. Pat. No. 3,306,737, column2, lines 61-69, and US. Pat. No. 3,030,205, column 2, lines 7-52). Themagnesium containing prealloy is generally used, in such processes, inthe form of solid pieces of the prealloy, which are first charged into asheet metal container which is used as the bell jar or plunging cup. Itis also known to, preferably, use the magnesium containing prealloy inthe form of a cylindrical ingot for the production of cast iron withspheroidal graphite. A further known proposal provides for the use, forthis purpose, of magnesium or magnesium alloys in the form ofsemicylindrical ingots or composite cylindrical ingots formed from aplurality of the semicylindrical ingots, formed from a plurality of thesemicylindrical ingots, as disclosed in German Gebrauchsmuster Pat. No.1,71 1,729.

The magnesium containing prealloys which are used for the production ofcast iron with spheroidal graphite, however, because of their chemicalcomposition, tend to separate into their component parts in the moltenstage and it is often difficult to obtain, after solidification, aningot having the most homogeneous composition possible with a constant,invariable chemical analysis throughout. In order to avoid the tendencyof the molten magnesium prealloys from separating into their componentelements during the solidification of the melt, relatively thin sheetsof the prealloys were prepared in a conventional manner in order toattain a fast rate of cooling of the prealloy, as disclosed in GermanPat. No. 1,142,444.

The casting of prealloys of the type discussed herein in the form, forexample, of ingots, calls for the need, in accordance with conventionalprocedures, for a substantially slower cooling of the melt, and as arule, results in the separation of the elements from the alloycomposition during the solidification of the melt. The use of themagnesium prealloys, in the form of pieces which are prepared bybreaking up relatively thin sheets of prealloy of the type disclosed inGerman Pat. No. 1,142,444, in the production of cast iron withspheroidal graphite, requires a) that large volumes of the necessaryamounts of the prealloy additive be used, b) that a large immersing jaror plunging cap be used for a relatively small bulk weight of prealloyand c) that the cast iron melt to be treated with the prealloy provide acomparably large surface area to provide access thereto for theprealloy. The latter requirement results, however, in the oftenundesirable, rapid'liquefication of the magnesium prealloy during theprealloy immersion process and in undesirably violent reactions,particularly of the magnesium rich prealloy in the treating ladle.According to proposals already known to those in the art, and asdisclosed for example in German Pat. No. 1,173,667, the conduct of thecasting operation can be influenced by the magnesium prealloy by varyingthe chemical composition of the prealloy and with the aid of differentcomponents of the prealloy, which components, at times, must be used,with respect to each other, in established proportional amounts.

For the production of cast iron with spheroidal graphite there is, froma technical point of view, the need for the use of prealloys whichcontain as much magnesium as possible, and, at the same time, highoperating temperatures. There can be thus obtained in a reliable andcontrollable casting operation a moreeffective utilization of theprealloy and an improvement in slag separation, so that with comparablesized prealloy charges larger amounts of cast iron can be treatedtherewith, or with comparable weight charges of the prealloy the castiron treating process can be conducted with a decrease (a) in theamounts of prealloy needed, (b) in temperature losses, and in the sizeof the immersing jar or plunging cup needed.

Those in the art, therefore, have sought procedures and techniqueswhereby shortcomings in the use of 1 magnesium containing prealloys inthe preparation of cast iron with spheroidal graphite could be overcome.

SUMMARY OF THE INVENTION The object of the present invention is toprovide magnesium containing prealloys in such form as to enable them tobe more effectively 'used in the production of cast iron with spheroidalgraphite.

Another object of the present invention is to produce cast iron withspheroidal graphite using a novel form of magnesium containing prealloy.

The essence of the present invention lies in the preparation of solid,compact prealloy ingots having a high magnesium content. The ingots areused in such compact ingot form in the treatment of cast iron melts forthe preparation of cast iron with spheroidal graphite. The compactingots are formed by casting molten prealloy around solid, prefabricatedpieces of prealloy, wherein the composition of the molten alloy and thatof the alloy in piece form are the same or similar.

The FIG. depicts a magnesium containing ingot during the process of itspreparation according to the present invention.

DETAILED DESCRIPTION OF THE INVENTION INCLUDING PREFERRED EMBODIMENT Forthe solution of the problems facing those in the an as indicated above,the present invention provides a process for the production of ingotsmade from magnesium containing prealloys which are suitable for use as alarge unitary mass in the treatment of cast iron melts, and whichundergo no separation of the component elements therein when used assuch compact ingots.

This process for the production of such compact ingots comprises thesteps of a. preparing prefabricated, solid pieces of magnesiumcontaining prealloy,

b. charging the solid pieces of the prealloy into a container or apermanent mold, which preferably has a cylindrical shape, with thedensest packing of such pieces in such container as possible,

c. casting a molten magnesium containing prealloy into the hollow spacesexisting between the densely packed solid pieces of alloy, and

d. fusing the edges of the solid pieces of prealloy with the moltenprealloy so as to thereby embed the individual pieces in an integrallycompact prealloy ingot upon the cooling of the composite article.

The molten magnesium containing prealloy which is used to prepare thecomposite ingot should preferably be one which has a chemicalcomposition which is the same as, or similar to,

,that of the magnesium containing prealloy which is used in piece form.

In conducting the process of the present invention relative to thepreparation of the compact ingots, it is expedient to use a casting moldof the type which is cylindrical in shape and open at one end. There canalso be used for this purpose, a simple sheet metal sleeve which isplaced on a casting support. The container walls. of a simple vessel ofthis type can be made, for example, of very thin, about 5 mm. sheetiron. In particular instances it my be expedient to quickly cool thewalls of the container and thereby remove the heat of the molten alloyin order to prevent the hot melt from breaking through the thin walls ofthe container.

According to a particularly preferred embodiment of the process of thepresent invention relative to the preparation of the compact ingots, theprocess can be conducted with or without the need for additional coolingof the ingot mold by using single or multicompartment ingot molds ofcommercial quality and made of materials such as cast iron, copper, andother fireproof materials. Using such techniques, containerless prealloyingots may be prepared which can be subsequently placed in containerswhich are more suitable for shipping and storage purposes, for example,in drums of metal, paper or plastic, and which protect the ingotsagainst external factors.

In many instances it may also be expedient to insert a sheet metalsleeve in the ingot mold which would serve as an outer mantle for theprealloy ingot to be produced in the mold in order to, above all,prevent the possibility of breakage occurring when preparing ingots ofrelatively large weight. Finally, it is also advantageous, to cast intothe prealloy ingot a hanger device, for example, an iron hook, whichwill facilitate the insertion and fastening of the prealloy ingot in thedipping bell or cup.

The production of the prealloy ingots according to the present inventionis accomplished in the following manner. F Irst, pieces of aprefabricated magnesium containing prealloy are charged into thecontainer or mold provided for this purpose. To this end it is expedientthat the manner of charging or packing the pieces of prealloy into themold be conducted in a particular way using a particular sequence ofsteps. The packing procedure can be illustrated with reference to thedrawing accompanying this specification.

Referring to the drawing therefore the sequence of steps to be followedin charging the ingot mold is a. Three to four pieces of prealloy 1,each of which has about a 30-60 mm. average diameter are charged intothe bottom of cylinder 6 which is positioned on casting support 5.Cylinder 6 is a sheet metal sleeve open at the top and bottom thereof.The bottom opening of cylinder 6 is completely sealed from atmosphere bycasting support 6. Casting support and the cylinder 6 are made of fireresistant materials which are inert with respect to the prealloy to becharged into cylinder 6.

b. One or more pieces of prealloy 2, in the form of sheets are thenplaced on top of pieces 1 so as to form a pallet at the base of cylinder6, the top or potential load bearing surface of which pallet occupiesabout three-fourths to four-fifths of the cross-sectional area ofcylinder 6. The space in cylinder 6 between casting support 5 and thetop of piece 2 represents about percent to percent of the total volumeof cylinder 6.

c. Small sized pieces 3 of the prealloy, which have an average diameterof about l0-50 mm. are then charged into cylinder 6. They are supportedby the pallet formed by piece(s) 1 and 2, and fill the cylinder to heextent that pieces 1, 2 and 3 occupy about percent to 75 percent of thetotal volume of cylinder 6.

d. The empty spaces remaining in cylinder 6 after all of pieces 1, 2 and3 are charged therein are filled with molten prealloy 4.

Following this procedure one obtains a complete embedding of the packedpieces of prealloy as a result of the subsequent immersion thereof inthe molten prealloy 4 and thus there is obtained a quasimonolithic castingot of uniform composition which is capable of being easilytransported and stored.

The pieces 2 of the prealloy which are used to form the platform portionof the pallet thus form, in the entire prealloy ingot, a special type ofcore, which is surrounded by the other pieces of prealloy l and 3, aswell as by the molten prealloy 4.

Suitable starting materials which may be used for the prealloys arealloys having the following composition:

20-60 percent magnesium l-l0 percent calcium 20 percent iron 0-12percent rare earth metals l .5 percent impurities remainder silicon,which can be entirely or partially in the form of nickel and/or coppersilicides. 7

It has also been found to be expedient to use, for the one or more corepieces 2 of the ingot, an alloy the composition of which is differentfrom the composition of the molten prealloy. The difference in suchcompositions relates particularly to the presence in such core" piecesof certain alloy components which are used for the elimination orprevention of the undesirable influence which may be caused during thepreparation of cast iron with spheroidal graphite by the presence ofelements such as titanium, lead, antimony and bismuth in he cast ironmelt. This latter group of elements interferes with the formation of thegraphite in spheroidal form. The alloy used for the core pieces,therefore, differs from that used for the molten prealloy and the otherpieces of prealloy with respect to the rare earth metal content thereof,that is, the molten prealloy and the other pieces of prealloy contain,in this instance, magnesium as the only element responsible for inducingthe formation of spheroidal graphite and does not contain any, or onlynegligible quantities of, rare earth metals.

An alloy which is suitable for use in the formation of the core piecesof prealloy and which would contain rare earth metals has the followingcomposition:

30.8 percent magnesium 4.4 percent calcium 5.9 percent iron 10.6 percentrare earth metal 1.5 percent impurities remainder silicon.

Using a magnesium containing ingot with he rare earth metal salts onlyin the interior thereof, in the preparation of cast iron with spheroidalgraphite, provides the advantage that the rare earth metals are not usedin a desulfurization process together with the magnesium during theinitial portion of the treatment of the cast iron melt with themagnesium ingot. Rather, in essence, it is only the magnesium in theprealloy which is devoid of rare earth metals and which prealloy ispresent in preponderant quantities at this initial stage of thetreatment of the cast iron melt that is available and is used for thedesulfurization process. The magnesium sulfide slag, moreover, separatesfrom the molten cast iron much easier than the sulfide slag formed withrare earth metals.

There may be, therefore a functional nucleus or core present in theprealloy ingot made according to the process of the present invention,which core has a different composition, with respect to specificreactive materials such as the rare earth metals, than that of the mainbody of the prealloy ingot which surrounds such core. It can also beexpedient, on occasion to place, immediately on top of the load bearingpiece(s) 2 in the center of the ingot, and before the packing of thesmaller sized pieces 3 on top of piece(s) 2, an additional one or morepieces of prealloy having the same rare earth metal rich composition aspiece(s) 2. Finally, there can be used individual pieces 3 of prealloyin the center of the ingot which have an alloy composition, which isdifferent, with respect to the rare earth metal content thereof, thanthat of the prealloy pieces 1 and 2 and of the rest of the prealloypieces 3 and that of the molten prealloy 4, that is, the compositions ofall of the prealloys used in making the ingot is essentially the sameexcept the core piece.

The amount of molten magnesium prealloy which is to be used as theembedding melt is, expediently, substantially less than the amount ofmagnesium prealloy which is to be used in piece form. After the fusingof the edge regions of the prealloy pieces the molten prealloy veryquickly solidifies, since the readily available quantities of heat inthe molten prealloy are quickly absorbed by the pieces of prealloy and,in time, by the walls of the ingot container or mold. Following thisprocedure, the separation of the component elements of the ingot isavoided and no separation of such elements occurs. If the molten andpiece prealloy materials have the same chemical composition, then thereis thus produced an alloy ingot which, in analytical and metallurgicalrespects, is completely homogeneous in composition.

The cast ingot made from magnesium containing prealloys according to thepresent invention is particularly suitable for use in the dippingprocess treatment of cast iron which is used for the production of castiron with spheroidal graphite.

The process of'the present invention provides a number of advantages.For example, magnesium containing prealloys can be produced in the formof ingots of any desired technically useful size and with unusually goodhomogeneity of composition. A further advantage is to be noted in thatingot shaped and homogeneous prealloys with an unusually high magnesiumcontent can be produced, which, inspite of this unusually high magnesiumcontent and relatively low active surface area, assures a calm and safesequence of reaction and handling operations with comparatively greaterutilization of the magnesium content of such ingots in contrast to theuse of a prealloy of the same composition in piece form in the treatmentof cast iron.

in addition, a compact prealloy ingot can be produced ac cording to thepresent invention with a functional core for an economicallyadvantageous treatment of molten cast iron. The active elements of suchfunctional cores do not take part, to any practical extent, in theinitially occurring desulfurization reaction phase of the treatment ofthe cast iron melt and are entirely available for use in the subsequentspheroidal graphite formation phase of the production of cast iron withspheroidal graphite.

A more general advantage of the process of the present invention is alsoto be noted in that the magnesium containing compact prealloy ingotsmade according toe present invention allow for the use of comparativelysmaller dipping jars or cups. These smaller dipping jars are more stableand easy to handle and the use of these smaller dipping jars alsoprovides lower amounts of heat loss during the dipping process.

The volume of the prealloy ingots produced according to the presentinvention is not only substantially less than the corresponding amountof prealloy in piece form, but in addition, the prealloy ingot canprovide a higher magnesium content since the inherent and expectedgreater reactability of the prealloy, due to its high magnesium content,is compensated for by the reduction in the surface area of the ingot andthus a less violet running of the reaction is assured. By obtaining, inthis way, an almost invariable utilization of the entire magnesiumcontent of the ingot, there is also obtained a high utilization of allthe components of the prealloy.

A greater advantage of the process of the present invention relative tothe treatment of cast iron with the prealloy ingots can be also seen inthat the use of the prealloy ingots prepared according to the presentinvention for this purpose allows for the use of treatment temperatureswhich are substantially higher than those which may be employed whenusing prealloys of the same composition in piece form, which latterprocess, again, gives rise to problems involved in the variousrelationships between prealloy volume and prealloy surface area.

The processes of the present invention are further explained in thefollowing examples.

The following examples, however, are merely illustrative of the presentinvention and are not intended as a limitation upon the scope thereof.

EXAMPLE 1 A magnesium containing prealloy was produced in a conventionalmanner in a graphite crucible in an induction fur trace and was thencast in an open hearth into sheets which were 40-55 mm. thick. Theprealloy had the following composition: llltlllclll-l Percent gig 50. 9a 4. 8 SE* 0. 8 Fc "4. 6 Si Remainder After being cooled the prealloysheets were broken up into pieces ranging size from that of walnutstothat of the palm of a hand. into a container made of sheet iron and openat the top, 2.7 kg. of the broken up pieces of the prealloy were denselypacked. The container had a diameter of 250 mm. and its walls were 2.5mm. thick. The broken pieces of alloy occupied about 35 percent of thevolume in the container.

The remaining empty space in the container between the broken pieces ofprealloy was filled up by pouring in molten magnesium prealloy which wasslightly overheated. The molten magnesium prealloy was prepared byremelting a portion of the magnesium prealloy first described above inthis example and it had, therefore, the same chemical composition asEXAMPLE 2 Cast iron with spheroidal graphite was produced in a foundryusing the dipping process in two different experiments. In one of theexperiments there 5 used a commercially available magnesium prealloy inpiece form which had a magnesium content of 30.4 percent, and in theother experiment there was used the prealloy ingot produced in example 1which had a magnesium content of 50.9 percent. A magnesium prealloy inpiece form and having a high magnesium content comparable to that of theprealloy ingot made in example i does not lend itself to use in theintended process because of the danger of explosions.

Table I below gives a description of the compositions of the twoprealloys used and table II gives data relative to the use of the twoprealloys in the two experiments.

Prealloy used Commercial prealloy Example I prealloy Weight ofprealloy,kg. 6.2 Magnesium content, 30.4 50.9 Cast iron charge. kg. 1000 1000Cast iron charge analysis, 71

5 (Milli ll.0l7

Fe remainder remainder Dipping temperature 1485 C. l500 C. Dipping time50 seconds 55 seconds FeSi-QO-innoculation 5 kg. Si 5 kg. Si Analysis ofcast iron at beginning of casting & after dipping process,

Table ll-Continued The FeSi90 alloy for innoculation, ofa grain sizesfrom 2-6 mm. had the composition 90.5

l A], balance Fe. It was added to the melt after the treatment withmagnesium when typping the melt in the melt in the pouring ladle.

Based on the above noted analytical results it was determined that theyield", i.e., amount actually used, of magnesium and prealloy in each ofthe two experiments was as follows:

Experiment Commercial prealloy Treatment with Mg yield, 2 Prealloyyield, )2

Example I prealloy EXAMPLE 3 All the prealloy used in this Example, inpiece or molten form, had the following composition:

31.4 percent Mg. 4.5 percent Ca 7.1 percent Fe l .5 percent impuritiesremainder silicon A cylindrical sleeve 180 mm. high with a diameter of175 mm. and made of sheet iron about 2 mm. thick was stood on one of itsends on a cast iron plate. At the bottom of the sleeve a pallet likeform was erected by first setting three pieces of prealloy at the baseof the sleeve, resting on the cast iron plate. These three pieces ofprealloy were 30-50 mm. in particle size. These three pieces of prealloyfunctioned as legs for the pallet and correspond to pieces 1 shown inthe drawing. A platform forming piece of prealloy was then placed on topof the three previously positioned pieces of prealloy. The platformpiece corresponded to piece 2 shown in the drawing. The platform pieceoccupied about three-fourths of the cross-sectional area of the insideof the cylinder and it was about 35 mm. thick. On top of the platformpiece there was then poured pieces of prealloy which were to 50 mm. inparticle size. The total weight of prealloy used in piece form in thecylinder was now 4.5 kg.

Molten prealloy was then poured into the cylinder, which had beencharged with prealloy in piece form as described above, so as to fillthe hollow areas between the pieces and to cover the top layer ofpieces. After the molten prealloy had solidified a quasi-monolithicingot had been thus prepared from the molten prealloy and piece formprealloy which had a total weight of 8 kgflOO g. The weight of the blockwas very accurately determined using a scale as disclosed above. Thepieces of prealloy were bound into the ingot by the solidified moltenprealloy. The molten prealloy solidified very quickly due to the coolingeffect or heat absorbing action of the prealloy in piece form, so thatthe sheet metal cylinder did not melt away. The ingot was lifted off thecast iron plate and the base of the ingot was inspected. The inspectionshowed that the three pieces of prealloy that were first placed in thebase of the cylinder as legs for the pallet were still plainlydiscernible. They were inclosed by the solidified molten prealloy, withonly their surfaces, which were at the extreme base of the cylinder,being essentially free of any of the subsequently charged and solidifiedmolten prealloy. The ingot had excellent strength and was capable ofbeing readily transported.

EXAMPLE 4 A prealloy ingot which weighed 8 kg. was produced by theprocedure described in example 3. The procedure of example 3, however,was deviated from in that the prealloy piece which was used as theplatform forming piece of prealloy and which took up about three-fourthsof the cross-sectional area of the cylinder weighed about 800 grams andwas prepared from a prealloy having the following composition:

30.8 percent Mg.

4.4 percent Ca 5.9 percent Fe 10.6 percent SE* 1.5 percent impuritiesremainder Si *SE rare earth metal This prealloy composition differs fromthe prealloy composition used in example 3, in essence, only by virtueof a high rare earth metal content.

By using, as the molten prealloy for embedding the piece form prealloyin the resulting ingot, a prealloy having the composition as that usedin example 3, the finished ingot has the following average composition:

30-32 percent Mg 4.2-4.6 percent Ca 8 percent Fe about 1 percent SE 1.5percent impurities remainder silicon This is an alloy composition whichis generally used in the treatment of cast iron in the dipping process.

By using magnesium containing ingots made according to the presentinvention in the treatment of cast iron, one is assured that, during theutilization of the ingot in the cast iron, melt being treated therewith,at first a prealloy devoid of rare earth metals reacts with the moltencast iron and then only later does prealloy containing such rare earthmetal become available for use in the cast iron treating process. Thisleads to the result that the desulfurization phase of he treatment ofthe molten cast iron which takes place first, would only entail lossesof the Mg content of the prealloy and would not entail any significantlosses of the rare earth metal content of the prealloy.

A prealloy ingot made according to the present invention and asdescribed in example 4 was used in the treatment of molten cast iron inthe clipping process. The charge of molten cast iron weighed 1,000 kg.and had a sulfur content of 0.06 percent and a temperature of 1480 C.After the treatment, which lasted for about 1 minute, the molten castiron was almost free of sulfur, i.e., it had a sulfur content of 0.006percent, and the Mg content of the molten cast iron amounted to 0.068percent. An adequate alloy content is thus assured to um containingprealloy comprising a. densely packing a substantial portion of thevolume of a cope with some of the disturbing influences that the castiron will encounter during itsperiod of use.

All percentages used in this application are in terms of perl. A processfor the production of an ingot from a magnesimold with a plurality ofsolid pieces of a magnesium con taining prealloy,

b. filling the remaining void spaces in said mold with a moltenmagnesium containing prealloy so as to fuse the edges of said pieces,said pieces of prealloy and said molten prealloy being of essentiallythe same chemical composition, and

c. cooling sad molten prealloy and said solid pieces of prealloy to forma composite ingot wherein said pieces of prealloy are embedded in saidmolten prealloy.

2. A process in claim 1 in which said mold has an internal volume ofabout 0.05 to 3 cubic feet.

3. A process as in claim 2 in which said solid pieces occupy about 25 to75 percent of the space in said mold.

4. A process as in claim 3 in which a) is accomplished by i. forming, inthe bottom of said mold, with'a relatively small number of said piecesofabout 30 to 60 mm. average diameter in size, a pallet having a loadbearing surface equal to about three-fourths to four-fifths of thecrosssectional area of said mold, and

loading the remainder of said pieces on said load-bearing surface, eachof the remainder of said pieces having an average diameter of about 10to 50 mm.

5. A process as in claim 4 in which all the prealloy used is of the typeused in the treatment of cast iron melts for the production of cast ironwith spheroidal graphite.

6. A process as in claim 5 in which all the prealloy has the composition2060 percent magnesium 1-1 0 percent calcium 20 percent iron 0-12percent rare earth metals 1.5 percent impurities remainder siliconcontaining materials selected from the group consisting of silicon andnickel and copper silicides.

7. A process as in claim 5 in which said ingot is formed with a corehaving a composition different from that of the remainder of said ingotby using for said core prealloy in piece form having the compositiondesired forsaid core.

8. A process as in claim 7 in which said core is formed from prealloycontaining magnesium and rare earth metals.

2. A process in claim 1 in which said mold has an internal volume ofabout 0.05 to 3 cubic feet.
 3. A process as in claim 2 in which saidsolid pieces occupy about 25 to 75 percent of the space in said mold. 4.A process as in claim 3 in which a) is accomplished by i. forming, inthe bottom of said mold, with a relatively small number of said piecesof about 30 to 60 mm. average diameter in size, a pallet having a loadbearing surface equal to about three-fourths to four-fifths of thecross-sectional area of said mold, and loading the remainder of saidpieces on said load-bearing surface, each of the remainder of saidpieces having an average diameter of about 10 to 50 mm.
 5. A process asin claim 4 in which all the prealloy used is of the type used in thetreatment of cast iron melts for the production of cast iron withspheroidal graphite.
 6. A process as in claim 5 in which all theprealloy has the composition 20-60 percent magnesium 1-10 percentcalcium <20 percent iron 0-12 percent rare earth metals <1.5 percentimpurities remainder silicon containing materials selected from thegroup consisting of silicon and nickel and copper silicides.
 7. Aprocess as in claim 5 in which said ingot is formed with a core having acomposition different from that of the remainder of said ingot by usingfor said core prealloy in piece form having the composition desired forsaid core.
 8. A process as in claim 7 in which said core is formed fromprealloy containing magnesium and rare earth metals.